How we cite our quotes: Citations follow this format: (Act.Scene.Line). Every time a character talks counts as one line, even if what they say turns into a long monologue.
Quote #1
MARY
I'm not blaming you, dear. How can you help it? How can any one of us forget? (1.1.228)
Mary's argument here is that Edmund can't be blamed for being suspicious of Mary, since the past cannot be forgotten. See the quotes on "Fate and Free Will" for more on the past's influence on the present.
Quote #2
MARY
Bitterly.
Because he's always sneering at someone else, always looking for the worst weakness in everyone.
Then, with a strange, abrupt change to a detached, impersonal tone.
But I suppose life has made him like that, and he can't help it. None of us can help the things life has done to us. They're done before you realize it, and once they're done they make you do other things until at last everything comes between you and what you'd like to be, and you've lost your true self forever. (2.1.76)
Once again, under the influence of morphine, Mary abandons the blame game, recognizing that getting mad at Jamie logically leads to her blaming herself for poor decisions she made in her past (such as, perhaps, marrying James or having Edmund). That's why she says "you lose your true self": she attributes the blame of her past actions to a self that wasn't essentially her, a self that came about due to bad circumstances.
Quote #3
MARY
In a real home one is never lonely. You forget I know from experience what a home is like. I gave up one to marry you – my father's home. (2.2.3)
This is an interesting line – yes, Mary's doing her classic "my life changed when I married James and now it's way worse" shtick, but check out how she's positioning James relative to her father. We see here the makings of another important theme for Mary: James is expected to do the double duty of husband and father for Mary. When Mary married James, he became a stand-in, a replacement for her dead father. This pressure on James is intense, and he (perhaps reasonably) fails to live up to her demands.